Petroleum residues, i.e. solid residues from the processing of petroleum, which can be formed during the petroleum-processing operation or upon combustion, and which can contain comparatively large quantities of vanadium and nickel at least in part resulting from the presence of vanadium and nickel in petroleum-processing particles.
It has been proposed to comminute such residues and combine the comminuted residues with alkali compounds and to roast the resulting mixture in an oxidizing atmosphere in a roasting furnace to obtain a solid composition which could be leached or extracted with water. The vanadium and nickel could be recovered from the resulting solution.
Generally the residues in question arise from their treatment and utilization of vanadium- and nickel-containing crude oils and petroleum products in coking, hydrodemetallization, cracking, gasification and combustion.
Such residues can contain 10 to 60% by weight V.sub.2 O.sub.5 and 3 to 15% by weight Ni apart from similar but conventionally present amounts of Mg, C, Si, Ca and S. Vanadium- and nickel-containing catalysts are generally required for the production of fats and waxes, for the hardening of fats by hydrogenation and in heavy oil processing.
The roasting which has been described does not yield products permitting differentiated processing to recover nickel compounds on the one hand and vanadium compounds on the other. In general, therefore, compounds of both vanadium and nickel are recovered together and separation poses a problem if it is necessary.
Because there have been only limited ways in which these residues could be processed economically and to obtain valuable components therefrom, it has generally been less expensive or more cost effective to dispose of the residues in landfills, rather than attempt to recover either the nickel or the vanadium therefrom.
In more general terms, it may be noted that the art has recognized a number of processes for the processing of nickel-containing and vanadium-containing materials but that these have seldom found their way into large scale use in practice. One proposal subjects the material to a reduction of vanadium oxide in an electric furnace for the production of ferro vanadium. Because of the high content of sulfur, carbon, nickel and silicon in such materials, the ferro vanadium which is produced is treated as second grade and thus has limited utility. It has also been proposed to subject the entire mass to a reducing operation which is followed by separation of vanadium by precipitation or extraction. We are not aware of commercial utilization of this procedure.
The use of alkali roasting as a means of treating petroleum residues, like proposed acid treatment, has also been found to be of limited utility and usually has been believed to be desirable only in association with nickel-free slags, because a high nickel content of the roasted material detrimentally affects waste water treatment, i.e. the treatment of waste water formed in the process which cannot be discharged because of the heavy metal content into the environment.